Electronic line printers generaly utilize a platen and rotating helix which contacts the surface of specially coated paper and, when electrically activated by a suitably high voltage, the paper darkens resulting in a visible image.
The printed paper emerges from an egress slot of the printer. Electromagnetc interference (EMI) noise generated within the printer, and particularly the noise generated by the high voltage in the helix to platen (ground) region, which is required in the printing process to remove the front coating from the conductive paper, is a source of EMI contamination to the surrounding region.
It is necessary to reduce the residual voltage on the paper, so that a very low level remains, in order to bring the EMI contamination to acceptable limits, as determined by testing methods long established in the industry.
The common prior art approaches to reduce residual noise on emerging conductive papers or tapes involves the use of conductive (usually metallic) brushes or fingers or by using pressure rollers (which are grounded), as well as EMI baffles for the higher frequencies. However, as restrictive (stationary fingers or brushes) devices are placed in the paper path, it becomes more difficult to exit the paper without paper jams. Rotating conductive rollers require considerable (pressure) force to effectively ground the paper, causing problems associated with paper feed and paper "metering". As an example, if the force is excessive the pressure rollers become driving members, causing paper to rip at the sprockets as this force overtakes the sprocket forces which previously were controlling the paper feed rate. Thus, slip clutches must be used in one of these driving mechanisms to avoid "kinematic" duplication of function with the resultant system failure (i.e. shredded or crumpled paper). The system becomes complicated, space and weight are consumed, and more power is required.